System for monitoring a swimming pool to prevent drowning accidents

ABSTRACT

A system for monitoring a swimming pool to prevent drowning accidents includes sensing devices (D1, D2, D3) for providing electrical signals forming images of bodies immersed in the pool water. Appropriate hardware (10) digitizes the resulting images, and the digital image data is compressed and stored at a series of times. Digitized images of a single body are compared at a series of times. The nature of a body, the path of the body and changes in the position of the body are estimated on the basis of the series of images; and an alarm is activated should the path or movement of the body being observed give cause for concern.

The invention relates to a system for monitoring a swimming pool toprevent drowning accidents.

At present, the monitoring of swimming pools is either inexistent or iscarried out by human monitoring. This type of monitoring is a difficulttask which requires sustained attention and causes the individualsresponsible for it, in particular swimming instructors, to suffernervous fatigue. Indeed, further to the limitations inherent in anysystem relying on human intervention, for example loss of attention dueto fatigue or temporary distraction, the monitoring of swimming pools ismade very difficult because of the reflection of light from the surfaceof the water which is agitated, a phenomenon which makes it difficult toidentify visually a motionless body at a depth of a few meters. Theproblem of monitoring swimming pools arises primarily for swimming poolswhich are open to the public.

The risk of drowning in a swimming pool occurs primarily when a batheris not sufficiently capable of swimming, for example in the case of ayoung child or when a swimmer faints.

In the first case, if the swimming pool is monitored, the swimminginstructor or individuals close to the bather in distress have theirattention attracted by the bather himself, in particular because he willwave his arms while trying to stay on the surface. In the second case,however, the swimmer will lose consciousness without attractingattention from those on duty or those nearby. There are generally twopossible outcomes: either the bather exercises the respiratory movementby reflex, in which case his lungs will fill with water, leading toimmediate loss of consciousness, or alternatively reflex apnoea willtake place and some volume of air will stay trapped in the lungs. Ingeneral, a bather who has suffered this type of accident will sink tothe bottom but, less commonly, he may also float unconscious in acharacteristic position just below the surface of the water.

In the time when consciousness is lost, which marks the onset ofdrowning, an experienced lifeguard, in particular skilled in expired-airresuscitation, has about two to three minutes to give aid to the victim.If aid is given within this time, the victim will not generally sufferlong-term affects from the accident, possibly after staying in hospitalto clean out his lungs. In general, if aid is given between three andfive minutes after consciousness has been lost, a time whichnevertheless varies between individuals, the victim may still be savedbut there is a risk of some irreversible damage, in particular to thebrain. After five minutes, the risk of death becomes significant.

It has already been proposed, in U.S. Pat. No. 5,043,705, to use sonarfor monitoring a swimming pool. According to this device, at least onesonar transmitter/receiver is provided on the bottom of the swimmingpool, and a layer is monitored using this equipment. However, a deviceof this type has a considerable drawback because, in order to installthe sonar and connect it to the processing equipment which derivesinformation from the echoes which are received, it is necessary to routecables through the bottom of the swimming pool and below this bottom,which leads to an entirely prohibitive cost if the pool has already beenconstructed. Moreover, safety rules prohibit the use of voltages inexcess of 12 or 24 volts, depending on the country, close to the waterin a swimming pool, whereas it is necessary to use voltages of severalhundred volts in order to generate sonar pulses. Furthermore, the signalobtained with sonar includes echoes due to the swimming pool walls, andit is extremely difficult to eliminate the noise signal thus obtained inorder to make it possible to detect the signal corresponding to thesubmerged body of a drowning individual. In addition, sonar essentiallymakes it possible to identify the body of a drowning individual by thevolume of air which it contains; if a victim has his lungs filled withwater, the signal obtained will not at all conform with what might beexpected, and may even not be identified by the signal processing. Itwill therefore be understood that a system of this type cannot besatisfactory.

It has also been proposed, in patent application WO 95/34056, to usecameras working in the visible wavelength range to monitor a swimmingpool, these cameras being arranged in such a way that the observedregion lies in a volume close to and parallel with the bottom of theswimming pool. In this device, the cameras only observe a layer of waterparallel to the bottom, which means that the number of cameras needs tobe increased if the bottom is not flat, as well as leaving most of thevolume of the swimming pool unmonitored. Furthermore, this device doesnot make it possible to detect motionless bodies just below the surfaceof the water. Lastly, the cameras and their accessories are immersed inthe swimming pool, which is unacceptable in terms of safety and causesconsiderable problems in connecting them to the signal processingequipment associated with them. This device cannot therefore besatisfactory.

The object of the invention is to provide a system for monitoring aswimming pool, which makes it possible to operate an alarm whichautomatically warns the monitoring staff promptly when the behaviour ofa bather gives reason to suspect that he is at risk of drowning. Asystem of this type must be capable of detecting the start of a drowningaccident, but it is also desirable to avoid false alarms by correctlyanalysing the behaviour of the swimmers, in particular to avoid amisinterpretation relating to the movement of a swimmer whose isintentionally diving and/or swimming under water. A further object ofthe invention is to describe a device of this type which can beinstalled without excessive costs in a swimming pool which has alreadybeen constructed. Another object of the invention is to describe adevice of this type which is inaccessible to the users of the swimmingpool and meets all safety requirements. A last object of the inventionis to describe a device of this type which can be maintained andserviced easily without needing the swimming pool to be drained.

According to the invention, a system for monitoring a swimming pool toprevent drowning accidents, is characterized in that it comprises:

detection means which can give, in the form of the electrical signals,images of bodies immersed in the water of the swimming pool, thesedetection means being provided on the walls of the swimming pool atpoints which are expediently distributed in order to scan at least afraction of the volume of water in the swimming pool;

means for digitizing the electrical signals which are obtained;

means for compressing the digital data obtained by the aforementioneddigitizing means;

means for temporary and permanent storage of the digital data pertainingto images at successive times;

means for comparing the digitized images pertaining to the same body atsuccessive times;

means for assessing the nature of a body (whether or not it is a humanbody), the path and changes in attitude of the body on the basis ofthese successive images; and

decision means which can operate alarm means should the path or movementof the body being observed give cause for concern.

Preferably, each detection means comprises at least one video cameraarranged in a watertight compartment supported by a side wall of theswimming pool, between the surface of the water in the swimming poolwhich is being used and the bottom of the said swimming pool; since thewatertight compartment is below the surface of the water, provision maybe made for an anti-moisture module to be arranged inside the saidwatertight compartment. Advantageously, the watertight compartment isimmersed and contains two video cameras, the conical observation fieldsof which have an aperture angle of about 90°, and the axes of which aresubstantially orthogonal in a substantially horizontal plane.

Advantageously, use is made of means for multiplexing the electricalsignals delivered by the detection means, these multiplexing meansfeeding the digitizing means; the said digitizing means and the meansfor compressing the digital data advantageously consist of a card fordigitizing and compressing video images which is placed in amicrocomputer with multimedia configuration.

The means for temporary and permanent storage of the digital datapertaining to images at successive times, the means for comparing thedigitized images pertaining to the same body at successive times, themeans for estimating the path and changes in attitude of a body and thedecision means consist of the components of a microcomputer, inparticular memory elements and the central processing unit of thismicrocomputer, in which suitable software has been loaded in order toallow it to perform the operations which have been indicated.

Advantageously, the digitizing means make it possible to digitize 25images per second, these images being supplied by the detection meansvia the multiplexing means.

The means for comparing the digitized images between successive timesare capable of taking into consideration only images whose dimensionscorrespond at least to those of a child, in order to exclude falsealarms which may be caused by foreign bodies. These comparison means arefurthermore designed to isolate a shape and track its path at successivetimes.

The estimation means are capable of determining, on the basis of theresults of the comparison means, that a human body in the swimming poolis moving slowly and/or is motionless.

The decision means are capable of operating an alarm if the body in theswimming pool continues to move slowly or remains substantiallymotionless for more than a determined time, in particular more than 15seconds.

Advantageously, the images which were used for the analyses leading to awarning being given are recorded on the hard disk of the microcomputerso that they can be consulted at any time.

Preferably, one or more monitor screens are arranged close to the seatsof the swimming instructors or in the rooms of the staff in charge ofmonitoring the swimming pool, on which screens the images of a regionconsidered as giving cause for concern are displayed.

The alarm may be given by an audible and/or visual warning device, inparticular with an indication of the region of the swimming pool inwhich an event giving cause for concern is taking place.

It is possible to provide a device for immediately shutting down thepumping and filtration of the water in the swimming pool should anaccident be detected, it being possible for this shutdown device to becontrolled either manually or automatically by the microcomputer.

Advantageously, the detection means are each arranged in a watertightcompartment, one wall of which consists of a globe having regionsthrough which the information is acquired, making it possible to producethe images of the bodies immersed in the water in the swimming pool, andanother wall of which is passed through in watertight fashion by cableswhich convey the information supplied by the detection means to outsidethe swimming pool. The wall through which the cables pass is equippedwith a first removable watertight connector, connected to the first endof a watertight sheet whose other end is connected to a secondwatertight connector fixed to the end of a casing which passes inwatertight fashion through the side wall of the swimming pool. Provisionis preferably made that the interior of the casing is in communicationwith the water in the swimming pool, and that the leaktight sheath iscoiled in the casing so as to have a length at least equal to that whichmakes it possible to remove the compartment from the water in theswimming pool without detaching the watertight connector fixed to theend of the casing.

Apart from the arrangements explained above, the invention consists of acertain number of other arrangements which will be dealt with moreexplicitly below with regard to a non-limiting illustrative embodimentwhich is described with reference to the appended drawing.

In this drawing:

FIG. 1 is a schematic perspective view of a swimming pool equipped withthe detection means of a monitoring system according to the invention;

FIG. 2 is a schematic plan view of the swimming pool, illustrating thefields of view of the detection means which scan the entire volume ofwater in the swimming pool;

FIG. 3 is an elevation view of an immersed globe containing a detectionmeans of the monitoring system according to the invention;

FIG. 4 is a view in section on the line IV--IV in FIG. 3;

FIG. 5 is an enlarged view of the detail A in FIG. 4;

FIG. 6 is a view in section on the line VI--VI in FIG. 4;

FIG. 7 is an enlarged view of the detail B in FIG. 6;

FIG. 8 is a perspective view of the globe in FIG. 3;

FIG. 9 is a simplified block diagram of the monitoring system.

As illustrated in FIG. 1, the system for monitoring a swimming pool Pcomprises detection means D1, D2, D3 provided on the walls of theswimming pool at points which are expediently distributed in order toscan the entire volume of water in the swimming pool. In the example inquestion, the three detection means D1, D2, D3 are arranged in the samehorizontal plane, for example at a level of about 1.50 m below the levelof the water in the swimming pool which is being used. As illustrated inFIG. 2, the detection means D1, D2, D3 are arranged in such a way thattheir fields of view partly overlap so as to leave no blind region andto scan substantially the entire volume of the swimming pool. An elementor a body situated in the swimming pool will therefore be seen by atleast two detection means D1, D2, D3.

These detection means are capable of producing, in the form ofelectrical signals, images of bodies immersed in the water of theswimming pool.

The detection means D1, D2, D3 are all identical and one of them, D1,will be described in detail below. The means D1 comprises two videocameras 1 and 2, preferably electronic cameras of the CCD type. The axesof the two cameras form an angle of 90° with one another and aresymmetrical with respect to a plane which is perpendicular to the wallof the swimming pool and passes through the axis of the detection means.The aperture angle of the field of view of each of the cameras 1 and 2is greater than 90°, and one of the borders of the field coincidesapproximately (seen in plan) with the pool side which supports thedetector, so that, for the two cameras taken in combination, the fieldof view (seen in plan) is 180° with a central region α, β, γrespectively for the detection means D1, D2, D3 where there is anoverlap between the fields of the two cameras. In the example which isdescribed, the detection means D2 is supported by the side wall 100 ofthe swimming pool P adjacent to the deep end, at the point B on the saidwall 100 lying in the longitudinal mid-plane of the swimming pool,whereas the detection means D1 and D3 are supported at A and C by thetwo longitudinal walls 101, 102 of the swimming pool, level with theinclined bottom region 103 joining the shallow end to the deep end,points A and C being in the vicinity of the transverse mid-plane of theswimming pool P. FIG. 2 schematically represents the observation conesof the two cameras of each detection means, denoting the cones of thecameras of the detection means D1 by a1, a2, those of the detectionmeans D2 by b1, b2 and those of the detection means D3 by c1, c2. It cantherefore be seen that the majority of the regions in the swimming poolare covered several times by the detection means: the monitoring takesplace three-dimensionally since each camera has an observation cone,whereas in the prior art WO 95/34056, it was only possible to monitor alayer of water close to the bottom. Nevertheless, there are regions ofwater above and below each detection means which are covered only twice.The field of each camera encroaches by a small angle e on the pool sidewith which the said camera is associated, which reduces the linedregions that the observation by the cameras does not cover.

The cameras 1 and 2 are arranged in a globe 3 which is closed inwatertight fashion and, as indicated below, is supported by the wall 4of the swimming pool. A cylindrical duct 5 passes through this wall 4and accommodates a cylindrical casing 7 containing a tubular sheath 8 inwhich the electrical cables 8a are arranged which connect the cameras 1and 2 to the microcomputer 9 managing the system for monitoring theswimming pool. The sheath 8 is wound in a coil along the wall of thecasing 7 and its ends are secured, by watertight connectors 20 and 24,respectively to the end 7a of the casing 7 and to a bell 23 associatedwith a compartment 21 which will be defined below. The compartment 21 iswatertight; the bell 23 is attached in watertight fashion to thecompartment 21; the interior of the bell 23 is connected to the exteriorof the casing 7 by the sheath 8.

The two cameras 1 and 2 are oriented at about 90° relative to oneanother and their axes lie substantially in a horizontal plane. In theexample in FIGS. 3 to 8, the globe 3 is rounded in order to avoid anyinjury to a swimmer who comes into contact with the said globe. Theglobe 3 is moulded from cast aluminium; in front of the cameras 1 and 2,it has two circular orifices where two lenses 1a, 2a are set in, theselenses cooperating with the objectives of the two cameras 1, 2respectively to form "objective assemblies"; the rim of each lens formsa collar which is bonded adhesively into a circular recess of the globe.The lenses are made of high-strength glass to prevent any risk ofdamage; the design of the lenses 1a, 2a makes it possible to adapt theoptical characteristics of the "objective assemblies" to therequirements of the system.

The duct 5 passing through the cycle 4 of the swimming pool is producedby boring; the cylindrical casing 7 is fitted in it and centring iscarried out using two O-ring seals 90, 91. The seal 91 located next tothe swimming pool has two holes, one in the vicinity of the bottom pointand the other in the vicinity of the top point. A polymerizable resin isinjected through the lower hole in order to form packing 6 between theduct 5 and the casing 7. After polymerization, the front face of thepacking 6 is completed, on the side facing the swimming pool, by fittinga silicone seal 6a.

The casing 7 is intended to be filled by the water of the swimming pool.The cameras 1 and 2 are housed in the watertight compartment 21, one ofthe faces of which, on the side facing the swimming pool, consists ofthe globe 3, while the other face, on the side facing the end 7a, isdefined by a cylindrical dish 21a, the free end of which supports aperipheral collar 21b. When the cameras have been installed in thecompartment 21, the globe 3 is fixed on the collar 21b by means ofscrews which cooperate with threaded bushes fitted in bores which areprovided through the thickness of the base 3a of the globe 3. Screwingthe said screws in compresses an annular seal 3b which makes theassembly watertight. The bottom 21c of the dish 21a supports anelectronics card 92 to which the output wires of the cameras 1 and 2 areconnected. The output of the said electronics card passes in watertightfashion through the bottom 21c which, on its outer face, supports afemale connector 93. The bottom 21c furthermore supports two valveconnectors 94, 95 intended to cooperate with a nitrogen feed tube, onthe one hand, and a venting tube on the other hand. It is thus possible,when the compartment 21 has been closed by attaching the globe 3 and thedish 21a, to create a dry nitrogen atmosphere in the interior of thecompartment in order to prevent oxidation, increase the life of the CCDcameras and prevent any fogging problem; once the tubes have beendisconnected, the valves of the connectors 94, 95 isolate the interiorof the compartment 21 from the outside. The bell 23, which is secured tothe bottom 21c by its shoulder 23a, is arranged on the bottom 21coutside the compartment 21; the shoulder 23a bears against the bottom21c via an annular seal 23b which is compressed by screws.

Using screws 96a, a collar 96 is fixed on the flat end of the casing 7on the opposite side from the end 7a, this collar 96 being intended tocover the border of the bore in which the casing 7 is arranged, as wellas the region occupied by the packing 6. At its extremity on theopposite side from the end 7a, the casing 7 has three peripheral bosses7b which protrude towards the axis of the casing 7; threaded bushes areinserted into these bosses which cooperate with screws 25; the heads ofthe screws 25 bear on the peripheral lip 3c of the globe 3. Thewatertight compartment 21 is thus held relative to the casing 7;however, because of the thickness of the globe 3 in the region where thescrews 25 pass through it, a clearance has been formed between thecollar 96 and the lip 3c; similarly, a clearance has been formed betweenthe casing 7 and the part of the globe 3 which penetrates into it; theresult of this is that the water from the swimming pool penetrates thecasing 7 freely. It is therefore possible, from inside the swimmingpool, to detach the chamber (3, 21, 21a, 23) from the casing 7irrespective of the depth at which the detection means is located in thewater of the swimming pool.

The bottom of the bell 23 supports a watertight connector 24 whichfastens the sheath 8 on the bell 23. The electrical cables 8a are fittedinto the sheath 8 before the bell 23 is fastened on the bottom 21c ofthe dish 21a, and the cables 8a emerge behind the end 7a of the casing7, the end 7a being sealed at this feed-through by the watertightconnector 20. The length of watertight sheath 8 provided between thewatertight connectors 20 and 24 is sufficient for the chamber (3, 21,21a, 23) to be detached from the wall of the swimming pool and placed atthe edge of the swimming pool in order to carry out maintenance, repairor replacement. At the same time as the cables 8a, a preparatory thread,for example a nylon thread, is fitted into the sheath, this threadacting, in known fashion, as a "guide" intended to make it possible tointroduce an additional or replacement cable into the sheath 8 withoutit being necessary to detach the connector 20 and therefore drain thepool: it is actually sufficient to attach the new cable and a new nylonthread "guide" behind the end 7a, take the chamber (3, 21, 21a, 23) outof the water, take off the bell 23, detach the connector 93, pull thenylon thread which is located there through the thus freed end of thesheath 8 until the new cable and the new "guide" appear, dispose of thesaid nylon thread constituting the initial "guide", connect the newcable which has been fitted in place on the connector 93, reattach thebell 23 on the dish 21a, lower the chamber (3, 21, 21a, 23) back underthe water and fix it back on the face of the casing 7 using the screws25.

Furthermore, the same set of screws 25 can be used to hold a closure cap(not shown) of the casing 7 when the compartment (3, 21, 21a) has beenremoved, the bell 23 having been fixed beforehand in watertight fashionon that one of the faces of the said cap which lies on the side facingthe casing.

An anti-moisture module (not shown) is preferably provided inside thecompartment 21.

The cables 8a which pass through the casing 7 are coaxial cables which,via multiplexing means 10a, are connected to a microcomputer 9, forexample of the IBM compatible type, organized around a PENTIUMmicroprocessor [lacuna] on each cable 8a, a DC voltage is establishedwhich is intended to power the corresponding camera 1, 2, and the saidcamera sends a modulation on the cable 8a, this modulation constitutingthe signal to be processed. Before entering the multiplexing means 10a,the DC component is separated using the modulation means which deliverto the multiplexing means only the signal originating from the CCD typecamera. The microcomputer 9 comprises a central processing unit 13,temporary storage means, or random-access memory 11a, permanent storagemeans, or hard disk 11b, and a remote-control card 14 which can controlwarning means 15 or valves 16; it is further connected to a monitorscreen E, the said screen being a touch-sensitive screen allowingoperational control. The microcomputer 9 has a multimedia configurationand is equipped with a video capture card 10 constituting means fordigitizing the electrical signals delivered by the detection means D1,D2, D3, and means for compressing digital image data.

The images, in the form of electrical signals, are received via thedemodulation means and the multiplexing means denoted 10a overall, at arate of 25 images per second, by the video capture card 10 whichconverts them into digital images.

By virtue of the multiplexing, it is possible to process the detectionmeans D1, D2, D3 with the same video card 10. It should be noted thatthe number of detection means treated by the same card could be greaterthan three and, for example, equal to eight.

Means 11 are provided for storing the digital data pertaining to imagesat successive times t, (t+1) etc. The storage means 11 consist of thememory means of the microcomputer 9, in particular internalrandom-access memory means 11a and the hard disk b of the computer.

Means 12 are provided for comparing the digitized images of the samebody at successive times t and (t+1). The comparison means 12 are formedby the central processing unit 13 of the computer and suitable softwarestored in a range of the internal random-access memory 11a.

The time interval Dt between the two times t and (t+1) taken intoconsideration is sufficient, in the case of a swimmer's normal movement,for the differences between the two successive images to give evidenceof this type of movement; the time interval Dt is, however, as small aspossible so that a warning will be given without delay should thesituation give cause for concern. This interval Dt may be of the orderof a few tenths of a second.

Between two times t and (t+1) the comparison means calculate thedifferences between two matrices of successive images output by the samecamera.

The comparison means thus make it possible to obtain the regions ofchange between two images at successive times, that is to say theregions of movement between the two times in question.

The central processing unit 13 combined with suitable softwareconstitutes, further to the means for estimating the nature of a bodywhose image is obtained (whether or not it is a human body), the pathand changes in attitude of this body. The central processing unit 13 andthe software are furthermore intended to form decision means capable ofoperating an alarm should the path or movement of the body beingobserved give cause for alarm.

The software allowing the computer 9 and its central processing unit 13to fulfil the functions mentioned above may correspond to variousalgorithms.

Because the matrix of the initial image (an empty swimming pool) isknown, the various shapes moving in the pool which are picked up by thedetection means can be counted and tracked individually.

Using the principle according to which knowledge of the derivative of afunction and its initial value makes it possible to ascertain thefunction, it is possible to identify and track various shapes,corresponding to different bodies moving in the swimming pool, forexample F1, F2 . . . Fn.

A correction is made on the shapes which are tracked, in particular interms of size. This is because only those shapes whose dimensionscorrespond at least to those of a small child are considered. It is thuspossible to exclude the images of inert objects, with small dimensions,and avoid false alarms.

The change in the path of the various shapes F1, F2 . . . Fn in thereference frame of the swimming pool is tracked. Should a movement givecause for concern, in particular in the event of a slow downwardvertical movement which corresponds to passive sinking, or in the eventof lack of motion at the bottom of the pool, or alternatively in theevent of lack of motion just below the free surface of the water, thecorresponding shape F_(i) is set in prewarning status.

Expedient positioning of the detection means D1, D2, D3 relative to thebottom of the swimming pool ensures correct operation, with the entireswimming pool being covered by these detection means. A track shape F1 .. . Fn should ideally be able to disappear only "upwards", that is tosay by leaving the lower region of the swimming pool by rising, or byleaving the swimming pool.

If, after a predetermined time interval, advantageously about 15seconds, the tracked shape F1 has not changed from behaviour which givescause for concern, that is to say if the lack of motion at the bottom orthe slow vertical movement or the lack of motion close to the surfacehas continued for these 15 seconds without resuming a non-passive path,warning is given by the computer 9. The latter advantageously includes aremote-control card 14 capable of operating a variety of audible orvisual warning means.

For example, the computer may operate a vibrator or buzzer 15, inparticular worn on the belt of a swimming instructor responsible formonitoring the swimming pool. Furthermore, the region of the swimmingpool where the event leading to the warning took place may be indicatedon a liquid-crystal display screen, also carried by the swimminginstructor, in the form of an alphanumeric code, so that the swimminginstructor can quickly take action at the correct place.

Provision may furthermore be made for the computer 9 to cut off thevalves 16 removing water from the swimming pool in the event of awarning, in order to stop any suction effect at the water output grillslocated at the bottom of the swimming pool. It is furthermore possibleto have a facsimile message sent automatically to an emergency medicalservice.

Finally, the software which is used may make the microcomputer 9 storethe digitized images of the incident on hard disk 11b.

The examples given above do not imply any limitation, and other meansfor giving warning may be used.

Furthermore, the images of the region where the movement giving causefor concern takes place, including a body being motionless at the bottomof the swimming pool, are displayed on at least one monitor screen Eavailable to the monitoring staff.

With a system of this type, it is suitable to detect with absolutereliability all cases of movement giving cause for concern which maylead to a warning, but it is also necessary to avoid false alarms. Forexample, a shape consisting of a darker region in the bottom of theswimming pool may simply be a shadow of sufficient size created abruptlyby the sun. A false alarm should be avoided in the case of this type.

The use of one or more sonars, in particular high-frequency activesonar, in the detection means D1, D2, D3 makes it possible to removeambiguity of this type and, if appropriate, have secondary tracking ofthe paths of the shapes F_(i) in the same sequence as the one mentionedwith regard to detection means consisting essentially of cameras.

Detection means other than video cameras could be used, for examplethermal cameras.

It might be possible to remove ambiguity relating to a detected shapeusing means other than a sonar, for example with a laser.

Whatever the alternative embodiment which is adopted, the monitoringsystem according to the invention makes it possible to improve thesafety of swimming pools.

What is claimed is:
 1. A system for monitoring a swimming pool toprevent drowning accidents, which comprises:detection means (D1, D2, D3)comprising at least one video camera having a field of view, said atleast one video camera being provided on a wall of the swimming pool inorder to scan at least a fraction of the volume of water in the swimmingpool, said video camera being adapted to give, in the form of electricalsignals, images of bodies immersed in the water of the swimming pool;whereby there is no echo due to said swimming pool walls generated bysaid at least one video camera; means (10) for digitizing the electricalsignals which are obtained from said at least one video camera; means(11a, 11b) for temporary and permanent storage of the digital datapertaining to said images at successive times; means (12, 13) forcomparing the digitized images pertaining to the same body at successivetimes; means (12, 13) for assessing the nature of a body as to whetherit is a human body, and for assessing the path and changes in attitudeof the body on the basis of these successive images; and decision means(12, 13) adapted to operate alarm means (15) should the path or movementof the body being observed give cause for concern.
 2. A system formonitoring a swimming pool to prevent drowning accidents, whichcomprises:detection means (D1, D2, D3) comprising a plurality of videocameras each of which has an observation cone directed in a differentdirection from the other observation cones of the other video cameras,said video cameras being distributed on at least one wall of theswimming pool with the observation cones of the various video camerasoverlapping, said video cameras being adapted to give, in the form ofelectrical signals, images of bodies immersed in the water of theswimming pool; whereby there is no echo due to said swimming pool wallsgenerated by said video cameras; means (10) for digitizing theelectrical signals which are obtained from said video cameras; means(11a, 11b) for temporary and permanent storage of the digital datapertaining to said images at successive times; means (12, 13) forcomparing the digitized images pertaining to the same body at successivetimes; means (12, 13) for assessing the nature of a body as to whetherit is a human body, and for assessing the path and changes in attitudeof the body on the basis of these successive images; and decision means(12, 13) adapted to operate alarm means (15) should the path or movementof the body being observed give cause for concern.
 3. System accordingto claim 1, characterized in that each detection means (D1, D2, D3)comprises at least one video camera (1, 2) arranged in a watertightcompartment (21).
 4. System according to claim 3, characterized in thatthe watertight compartment (21) is immersed and contains two videocameras, the conical observation fields of which have an aperture angleof about 90°, and the axes of which are substantially orthogonal in asubstantially horizontal plane.
 5. System according to claim 1, furthercomprising means (10) for compressing the digital data obtained by theaforementioned digitizing means, and the means for digitizing the imageswhich are obtained and for compressing the digital data consist of acard (10) for digitizing and compressing video images which is placed ina microcomputer (9) with multimedia configuration.
 6. System accordingto claim 1, characterized in that the detection means (D1, D2, D3) feedthe digitizing means (10) via multiplexing means (10a).
 7. Systemaccording to claim 1, characterized in that the means (11a, 11b) forstorage of the digital data pertaining to images at successive times,the means for comparing the digitized images pertaining to the same bodyat successive times, the means for estimating the path and changes inattitude of a body and the decision means consist of the components of amicrocomputer (9), in particular memory elements (11a, 11b) and thecentral processing unit (12, 13) of this microcomputer, in whichsuitable software has been loaded in order to allow it to perform theoperations which have been indicated.
 8. System according to claim 7,characterized in that the means (12, 13) for comparing the digitizedimages between successive times are capable of taking into considerationonly images whose dimensions correspond at least to those of a child, inorder to exclude false alarms which may be caused by foreign bodies. 9.System according to claim 7, characterized in that the comparison means(12, 13) are designed to isolate a shape and track its path atsuccessive times.
 10. System according to claim 7, characterized in thatthe estimation means (12, 13) are capable of determining, on the basisof the results of the comparison means, that a human body in theswimming pool is moving slowly and/or is motionless.
 11. Systemaccording to claim 7, characterized in that the decision means (12, 13)are capable of operating an alarm if the body in the swimming poolcontinues to move slowly or remains substantially motionless for morethan a determined time, in particular more than 15 seconds.
 12. Systemaccording to claim 7, characterized in that the images which were usedfor the analyses leading to a warning being given are recorded on thehard disk (11b) of the microcomputer (9) so that they can be consultedat any time.
 13. System according to claim 1, characterized in that atleast one monitor screen (E) is accessible to the personnel monitoringthe swimming pool, on which screen the images of a region considered asgiving cause for concern are displayed.
 14. System according to claim 1,characterized in that the alarm means comprise an audible and/or visualwarning device (15), in particular with an indication of the region ofthe swimming pool in which an event giving cause for concern is takingplace.
 15. System according to claim 1, characterized in that itincludes a device (16) for immediately shutting down the pumping andfiltration of the water in the swimming pool should an accident bedetected, it being possible for this shutdown device to be controlledeither manually or automatically by the microcomputer (9, 14). 16.System according to claim 1, characterized in that the detection means(D1, D2, D3) are each arranged in a watertight compartment (21), onewall of which consists of a globe (3) having regions (1a, 2a) throughwhich the information is acquired, making it possible to give the imagesof the bodies immersed in the water in the swimming pool, and anotherwall (23) of which is passed through in watertight fashion by cables(8a) which convey the information supplied by the detection means (D1,D2, D3) to outside the swimming pool.
 17. System according to claim 16,characterized in that the wall (23) through which the cables (8a) passis equipped with a first removable watertight connector (24) connectedto the first end of a watertight sheath (8) whose other end is connectedto a second watertight connector (20) fixed to the end (7a) of a casing(7) which passes in watertight fashion through the side wall (4) of theswimming pool.
 18. System according to claim 17, characterized in thatthe interior of the casing (7) is in communication with the water in theswimming pool, and in that the leaktight sheath (8) is coiled in thecasing (7) so as to have a length at least equal to that which makes itpossible to remove the compartment (21) from the water in the swimmingpool without detaching the watertight connector (20) fixed to the end(7a) of the casing (7).
 19. Swimming pool equipped with the systemaccording to claim 1, characterized in that the detection means (D1, D2,D3) are arranged in such a way that their fields of view partly overlapso as to leave no blind region and to scan substantially the entirevolume of the swimming pool.
 20. A system according to claim 2, in whichsaid video cameras are fixed and are distributed about at least threewalls of the swimming pool.